Renewable energy sources, such as biofuels, provide a substitute for fossil fuels and a means of reducing dependence on petroleum oil. In light of its low cost and wide availability, biomass is often used as a feedstock. Biofuels are typically produced by subjecting the biomass to thermolysis such as, for example, by slow pyrolysis, fast pyrolysis, liquefaction, catalytic thermolysis or enzymatic conversion. The liquid product resulting from thermolysis of biomass separates into an aqueous phase and an organic phase. The organic phase is commonly referred to as bio-oil. Bio-oil is relatively soluble in water though a small amount of water may be retained. Bio-oil can be converted to liquid hydrocarbon fuels. It is desirable to maximize the yield of product boiling between from 80° F. to 1,000° F. Material that boils below 80° F. is considered a light gas. Material boiling above 1000° F. is considered a solid.
Bio-oil typically contains a high level of oxygenates. In order to be converted into renewable hydrocarbons, it is necessary for the bio-oil to be stabilized by removing the oxygen through hydrotreating. This process involves contacting the bio-oil with hydrogen under pressure and at moderate temperatures, generally less than 750° F., over fixed bed reactors. Hydrotreating the bio-oil makes it compatible with petroleum derived refinery streams. In order to stabilize the bio-oil and reduce the amount of hydrogen required in hydrotreating, it is desirable for the bio-oil to have a low oxygen content.
Production of bio-oil in the biomass conversion unit and hydrotreatment of bio-oil typically renders heavy materials and solids which form unwanted carbonaceous deposits, such as coke. These solids reduce the yield of bio-oil and are largely removed from the product after the converted biomass exits the biomass conversion unit. The remaining solids and high boiling material typically plug the biomass conversion unit and catalytic hydrotreating bed and reduce on-stream time. The run length between stoppages in the biomass conversion unit and hydrotreater is therefore often decreased due to the presence of such materials and solids. Methods for reducing the amount of coking in biomass conversion systems have therefore been sought.
It should be understood that the above-described discussion is provided for illustrative purposes only and is not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. Thus, none of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude each or any of the above-cited features or disadvantages merely because of the mention thereof herein.
Accordingly, there exists a need for improved compositions, systems, apparatus and methods useful in connection with increasing the liquid yields and reducing the deposition of materials which form unwanted carbonaceous deposits in a biomass conversion system having one or more of the attributes or capabilities described or shown in, or as may be apparent from, the other portions of this patent.